Methods of etching oxide, reducing roughness, and forming capacitor constructions

ABSTRACT

The invention includes methods in which one or more components of a carboxylic acid having an aqueous acidic dissociation constant of at least 1×10 −6  are utilized during the etch of oxide (such as silicon dioxide or doped silicon dioxide). Two or more carboxylic acids can be utilized. Exemplary carboxylic acids include trichloroacetic acid, maleic acid, and citric acid.

TECHNICAL FIELD

The invention pertains to methods of etching oxide, and to methods ofcleaning debris (such as solid-form etch by-products) from withinopenings. In particular aspects, the invention pertains to methods forreducing roughness induced on surfaces during cleaning of debris, and insome aspects the invention pertains to methods of forming capacitorconstructions.

BACKGROUND OF THE INVENTION

It is common to etch through various oxides during semiconductorprocessing. Exemplary oxides include silicon dioxide, and doped silicondioxide (such as, for example, borophosphosilicate glass (BPSG), andphosphosilicate glass (PSG)). Oxides are common in semiconductorprocessing due to their electrically insulative properties, and due totheir ease of formation (for instance, oxides can be formed asspin-on-dielectric materials, or by numerous deposition methods,including, for example, chemical vapor deposition (CVD) methods).

It is common for oxides to be formed over electrically conductive nodes,and for openings to subsequently be etched through the oxides to theelectrically conductive nodes to expose the nodes for subsequentprocessing. The openings are formed with etch chemistry which removesthe oxide. In some aspects, the openings can be formed with multipleetch chemistries. For instance, a first etch chemistry can be utilizedto create the openings, and a second etch chemistry can be utilized toclean debris that may have been formed by the first etch chemistry.

Problems can occur during formation of openings extending into oxides,in that one or more of the etch chemistries utilized during theformation of the openings can undesirably roughen the exposed oxidesurfaces. For instance, substantially planar oxide surfaces may beexposed to the etch chemistry utilized to etch oxide-containing debrisfrom within openings, and such surfaces may be undesirably roughened bysuch etch chemistry. Accordingly, it is desired to develop new methodsfor etching oxides.

SUMMARY OF THE INVENTION

In one aspect, the invention includes a method for etching an oxide. Theoxide is exposed to a mixture which includes an alcohol, fluoride ions,and one or more components of a carboxylic acid having an acidicdissociation constant of at least 1×10⁻⁶. For purposes of interpretingthis disclosure and the claims that follow, the dissociation constantsutilized herein are to be understood as being the dissociation constantswhich would be measured in water.

In one aspect, the invention includes a method for reducing roughnessinduced on a silicon-dioxide-containing surface during removal ofsilicon-dioxide-containing debris with a cleaning solution. The methodincludes incorporation within the cleaning solution of one or morecomponents of a carboxylic acid having an acidic dissociation constantof at least 1×10⁻⁶.

In one aspect, the invention includes a semiconductor processing method.A semiconductor substrate is provided. The substrate supports an oxide.At least one opening is etched to extend at least partially through theoxide. The etching leaves debris within the opening (the debris can be,for example, etch by-products). At least some of the debris is cleanedfrom within the opening. One or more components of a carboxylic acidhaving an acidic dissociation constant of at least 1×10⁻⁶ are utilizedduring such cleaning.

In one aspect, the invention includes a method of forming a capacitorconstruction. A semiconductor construction is provided. Thesemiconductor construction includes a conductive node and an oxide overthe node. The oxide consists essentially of silicon dioxide or dopedsilicon dioxide. An opening is etched through the oxide to expose theconductive node. The etching leaves debris within the opening (thedebris can comprise etch by-products). At least some of the debris iscleaned from within the opening. A solution containing an alcohol,fluoride ions and a carboxylic acid having an acidic dissociationconstant of at least 1×10⁻⁶ is utilized during such cleaning. After thecleaning, a first capacitor electrode is formed within the opening. Acapacitor dielectric is formed over the first capacitor electrode, and asecond capacitor electrode is formed over the capacitor dielectric andcapacitively coupled with the first capacitor electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic, cross-sectional view of a semiconductorconstruction at a preliminary processing stage of an exemplary aspect ofthe present invention.

FIG. 2 is a view of the FIG. 1 construction shown at a processing stagesubsequent to that of FIG. 1.

FIG. 3 is a view of the FIG. 1 construction shown at a processing stagesubsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 1 construction shown at a processing stagesubsequent to that of FIG. 2, and illustrates problems that can occur ifprocessing alternative to that of FIG. 3 is utilized.

FIG. 5 is a view of the FIG. 1 construction shown at a processing stagesubsequent to that of FIG. 3.

FIG. 6 is a view of the FIG. 1 construction shown at a processing stagesubsequent to that of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Exemplary aspects of the invention are described with reference to FIGS.1-6. Referring initially to FIG. 1, a semiconductor construction 10 isillustrated at a preliminary processing stage. The construction 10includes a semiconductor substrate 12. Substrate 12 can comprise, forexample, monocrystalline silicon lightly-doped with background p-typedopant. To aid in interpretation of the claims that follow, the terms“semiconductive substrate” and “semiconductor substrate” are defined tomean any construction comprising semiconductive material, including, butnot limited to, bulk semiconductive materials such as a semiconductivewafer (either alone or in assemblies comprising other materialsthereon), and semiconductive material layers (either alone or inassemblies comprising other materials). The term “substrate” refers toany supporting structure, including, but not limited to, thesemiconductive substrates described above.

An isolation region 14 is formed within substrate 12. Isolation region14 can comprise, for example, a shallow trench isolation region.Accordingly, the isolation region 14 can comprise a trench formed withinsubstrate 12 and then filled with suitable dielectric material, such as,for example, silicon dioxide.

A transistor device 16 is supported by substrate 12. The transistordevice comprises a gate 18 containing conductive gate material 20 spacedfrom substrate 12 by gate dielectric 22. The gate dielectric 22 cancomprise, consist essentially of, or consist of, silicon dioxide.

The conductive gate material 20 can comprise any suitable composition orcombination of compositions, and can, for example, comprise metal, metalcompounds and/or conductively-doped semiconductor material such as, forexample, conductively-doped silicon.

The gate 18 also comprises a dielectric cap 24 formed over conductivematerial 20. Cap 24 can comprise, for example, silicon dioxide and/orsilicon nitride.

The transistor device 16 comprises source/drain regions 26 and 28 onopposing sides of the gate 18. The shown source/drain regions areconductively-doped diffusion regions extending within substrate 12. Suchdiffusion regions can comprise p-type doped regions and/or n-type dopedregions. The shown regions contain heavily-doped portions 30 and 32, andlightly-doped extensions 34 and 36 which extend between theheavily-doped portions and the edges of gate 18. A channel region 38 isbeneath gate 18 and between the source/drain regions 26 and 28. Inoperation, the source/drain regions are electrically coupled to oneanother through the channel region when appropriate current passesthrough the gate.

A conductive pedestal 40 is formed over source/drain region 28 andelectrically-coupled to such source/drain region. The conductivepedestal can comprise any suitable electrically conductive compositionor combination of compositions. In some aspects, the pedestal willcomprise conductively-doped silicon. The conductive pedestal has anuppermost surface 41 which can be referred to as an electricallyconductive node in some aspects of the invention.

The exemplary processing described herein ultimately forms a capacitorconstruction coupled to diffusion region 28 through pedestal 41 to forma dynamic random access memory (DRAM) device comprising transistor 16and the capacitor. The diffusion region 26 can be electrically coupledto a bitline so that the DRAM device can be incorporated into a DRAMarray. Various methodologies for coupling diffusion region 26 to abitline will be recognized by persons of ordinary skilled in the art,and such methodologies are not discussed in detail in this disclosure.Accordingly, various conductive materials that can be formed overdiffusion region 26 for ultimately coupling the diffusion region to thebitline are not described or shown. It is to be understood, however,that a conductive pedestal similar to the pedestal 40 can be formed overdiffusion region 26 in some aspects of the invention. It is also to beunderstood that numerous methods are known for coupling a capacitor to adiffusion region, and that some of the methods eliminate the conductivepedestal 40 and instead couple a storage node of the capacitor directlyto the diffusion region. Thus, although the invention is describedutilizing the conductive pedestal 40 between a capacitor (describedbelow) and the diffusion region 28, it is to be understood that theinvention also encompasses aspects (not shown) in which the conductivepedestal 40 is omitted and the capacitor is instead directly coupled tothe diffusion region.

Sidewall spacers 42 are shown formed along sidewalls of gate 18. Thesidewall spacers can comprise any suitable electrically insulativecomposition or combination of compositions, and typically will compriseone or both of silicon nitride and silicon dioxide. The conductivepedestal 40 is electrically isolated from conductive gate material 20 byone of the sidewall spacers.

An electrically insulative material 44 is provided over substrate 12,over transistor construction 16, and over conductive pedestal 40.Material 44 can comprise any suitable composition or combination ofcompositions. In particular aspects, material 44 will comprise, consistessentially of, or consist of silicon dioxide and/or doped silicondioxide. For instance, material 44 can comprise BPSG, PSG, and/orsilicon dioxide formed from tetra-ethyl-ortho-silicate (TEOS). One ormore compositions of material 44 can be formed by chemical vapordeposition, and/or as spin-on-dielectrics. It is to be understood thatthe insulative material 44 can, in some aspects, comprise a non-oxideinsulative composition in addition to one or more oxide insulativecompositions. For instance, insulative material 44 can comprise a layerof silicon nitride in addition to one or more layers ofsilicon-dioxide-containing compositions.

A patterned mask 46 is formed over insulative material 44. Mask 46 cancomprise, for example, photolithographically patterned photoresist. Mask46 has an opening 48 extending therethrough. The opening is directlyover the conductive node corresponding to surface 41 of pedestal 40.

Referring next to FIG. 2, opening 48 is extended through insulativematerial 44 with a suitable etch to expose the conductive nodecorresponding to uppermost surface 41. The etch can be any suitable etchknown in the art. For instance, if material 44 consists of one or moresilicon-dioxide-containing compositions, the etch can utilize CF₄/H₂.The etch forms debris 50 within the opening 48.

Referring next to FIG. 3, the debris 50 (FIG. 2) is removed with asuitable subsequent etch in a cleaning step. The debris can comprise,consist essentially of, or consist of oxide, and generally willcomprise, consist essentially of, or consist of silicon dioxide and/ordoped silicon dioxide. In an aspect of the present invention, suchoxide-containing debris is removed with a mixture which includes atleast one carboxylic acid having an acidic dissociation constant of atleast 1×10⁻⁶. The mixture includes one or more components of thecarboxylic acid having an acidic dissociation constant of at least1×10⁻⁶, with such components being defined to be either the acid form ofthe carboxylic acid or a conjugate base form of the carboxylic acid.Typically, the total concentration of all of the components of aparticular carboxylic acid within a cleaning mixture utilized inaccordance with methodology of the present invention will be from about1 part per million to a solubility limit of the components in themixture.

Any carboxylic acids can be utilized, provided that the carboxylic acidshave the acidic dissociation constant of at least 1×10⁻⁶. For instance,the carboxylic acids can be mono-carboxylic acids, di-carboxylic acids,or carboxylic acids having three or more carboxylic acid groups.Ultimately, as discussed below, the carboxylic acids are utilized toreduce roughness on oxide-containing surfaces. It can be preferred toutilize carboxylic acids having more than one carboxylate group for suchroughness-reduction, in that such carboxylic acids can, in some aspects,produce a greater roughness-reduction effect than is produced bymono-carboxylic acids.

Exemplary carboxylic acids that can be utilized in accordance withaspects of the present invention are trichloroacetic acid (which has anacidic dissociation constant in water of 1.99×10⁻¹); maleic acid (whichhas an acidic dissociation constant in water of 1.5×10⁻²); and citricacid (which as an acidic dissociation constant in water of 6.6×10⁻⁴).

In some aspects, a cleaning solution can include a alcohol, fluorideions and water in addition to the one or more components of at least onecarboxylic acid having an acidic dissociation constant of at least1×10⁻⁶. The alcohol can be an alkyl alcohol, and in exemplary aspectscan comprise, consist essentially of, or consist of isopropyl alcohol.In some aspects, other organic solvents can be utilized in addition to,or alternatively to, the alcohol. Such other organic solvents caninclude, for example, ketones, ethers and esters.

Cations can be present in addition to the fluoride ions, and inexemplary aspects, the cations can consist essentially of, or consist ofammonium ions. It is to be understood that ammonium ions are exemplarycations, and that other suitable cations can be utilized eitheralternatively or additionally to ammonium cations.

An exemplary mixture for cleaning oxide-containing debris can be formedby mixing the following:

-   -   (1) isopropyl alcohol provided to be present in the final        mixture to concentration of from about 90% to about 99.9%, by        weight (and typically at least about 98%);    -   (2) hydrofluoric acid provided to be present in the final        mixture to a concentration of from about 0.03% to about 0.3%, by        weight;    -   (3) ammonium fluoride provided to be present to a concentration        in the final mixture of from about 0.02% to about 0.3%, by        weight;    -   (4) water; and    -   (5) one or more carboxylic acids having an acidic dissociation        constant of at least 1×10⁻⁶ provided to be present in the final        mixture such that a total concentration of components of the one        or more carboxylic acids is from about 1 part per million (ppm)        to a solubility limit of the carboxylic acids in the mixture.

The cleaning mixture prepared as described above will typically be asolution rather than other types of mixtures, (with other types ofmixtures including, for example, emulsions, and mixtures havingundissolved components therein).

The cleaning mixture is utilized to etch oxide-containing debris fromwithin the opening 48. Such etching can be conducted while maintainingthe cleaning solution at a temperature of from about 0° C. to about 75°C., under a pressure of anywhere from 0.01 atmospheres to greater than10 atmospheres, and with a treatment time of from 1 second to about 10hours. A typical treatment time is from about 1 minute to about 20minutes.

FIG. 3 shows construction 10 after cleaning has been conducted inaccordance with aspects of the present invention to remove debris fromwithin opening 48. The FIG. 3 construction shows opening 48 havingsidewalls 49 which remain relatively smooth after the cleaning step. Incontrast, FIG. 4 illustrates construction 10 at a processing stageidentical to that of FIG. 3, but diagrammatically illustrating an effectwhich can occur if the carboxylic acid having an aqueous acidicdissociation constant of at least 1×10⁻⁶ is left out of the cleaningsolution. Specifically, the sidewalls 49 have roughened surfaces formedby the impact of the cleaning solution on such sidewall surfaces duringthe cleaning of the debris from within the opening. It is found that theamount of roughening can be reduced by at least two, four or even fivefold by including the carboxylic acid with the aqueous acidicdissociation constant of at least 1×10⁻⁶ in the cleaning solution. Theamount of roughening was measured by atomic force microscopy as rootmean square (RMS) roughness.

In light of the dramatic reduction in roughening occurring throughincorporation of carboxylic acids having an acidic dissociation constantof 1×10⁻⁶ in a cleaning solution during removal ofsilicon-dioxide-containing debris, such incorporation can be consideredto be a method for reducing roughness induced onsilicon-dioxide-containing surfaces during such cleaning. This canprovide a significant advantage, in that the roughness induced duringthe cleaning can lead to numerous problems in controlling uniformity ofopening dimensions. If uniformity is not adequately controlled, devicesultimately formed within the openings can operate outside of desiredtolerances, and devices formed within adjacent openings can short to oneanother. Also, there can be poor interfaces formed between layersultimately provided within opening 48 and the sidewalls of the openingif excessive roughening of the sidewalls occurs.

A possible mechanism by which the carboxylic acid can reduce theroughness occurring along the sidewalls of the opening is as follows.By-products may accumulate and aggregate during an etch, and suchby-products may reduce an etch rate. The reduction in etch rate mayincrease the etch duration utilized to completely remove debris, and theincreased etch duration may lead to increased roughening of exposedoxide surfaces. The by-products may accumulate because there isinsufficient material within the cleaning solution to bind or dissolvethe by-products, (for example, due to the coefficient of solubility ofthe by-products). The addition of carboxylic acids having acidicdissociation constants of 1×10⁻⁶ or greater can help in dissolving theby-products. The addition of water can also help in dissolving theby-products, but such addition adversely impacts selectivity of the etchfor oxides. In contrast, addition of carboxylic acids having high acidicdissociation constants (i.e., acidic dissociation constants of at least1×10⁻⁶) does not have such adverse impact on the etch selectivity.

The mechanism is provided herein to assist the reader in understandingaspects of the present invention, and is not to limit the claims exceptto the extent, if any, that such mechanism is expressly recited in theclaims.

Referring next to FIG. 5, construction 10 is illustrated at a processingstep subsequent to that of FIG. 3. Specifically, masking material 46(FIG. 3) has been removed, and a first capacitor electrode 60 has beenformed within opening 48. Capacitor electrode 60 can comprise anysuitable composition or combination of compositions. In particularaspects, electrode 60 will comprise metal, metal compounds, and/orconductively-doped semiconductor material such as, for example,conductively-doped silicon. The electrode is shown formed only withinopening 48. Such can be accomplished by providing the electrode materialto extend over an uppermost surface of material 44 as well as within theopening, and subsequently subjecting construction 10 to planarization(such as, for example, chemical-mechanical polishing) to remove theconductive material from over material 44 while leaving the conductivematerial within the opening.

Referring next to FIG. 6, capacitor dielectric 62 is formed over firstcapacitor electrode 60, and a second capacitor electrode 64 is formedover the capacitor dielectric 62. Capacitor dielectric 62 can compriseany suitable composition or combination of compositions, and inparticular aspects will comprise, consist essentially of, or consist ofsilicon dioxide, silicon nitride, aluminum oxide, and/or various high-kdielectric materials. The second capacitor electrode 64 can comprise anysuitable composition or combination of compositions, and in particularaspects will comprise, consist essentially of, or consist of metal,metal compounds, and/or conductively-doped semiconductor material. Thesecond capacitor electrode 64 is capacitively coupled with the firstcapacitor electrode 60. Accordingly, the construction comprisingelectrodes 60 and 64 together with dielectric material 62 is a capacitorconstruction. Such capacitor construction is electrically coupled withsource/drain region 28 through conductive pedestal 40.

A bitline 70 is shown electrically coupled with source/drain region 26.Accordingly, the construction of FIG. 6 can be considered to be a DRAMunit cell configured to be incorporated within a memory array.

The shown aspect of the invention is but one of many applications formethodology of the present invention. For instance, the incorporation ofone or more of carboxylic acids having an acidic dissociation constantof at least 1×10⁻⁶ can be utilized during the initial etch to form anopening (such as, for example, the etch of FIG. 2), as well as, oralternatively to, utilization of the carboxylic acid during the cleaningstep. Also, although the shown opening extends entirely through one ormore oxide-containing compositions to a conductive node, it is to beunderstood that the invention encompasses aspects in which an opening isformed to extend only partially through one or more oxide-containingcompositions.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of etching an oxide, comprising exposing the oxide to amixture which includes an organic solvent, fluoride ions, and one ormore components of a carboxylic acid having an aqueous acidicdissociation constant of at least 1×10⁻⁶.
 2. The method of claim 1wherein the oxide consists of silicon dioxide or doped silicon dioxide.3. The method of claim 1 wherein a total concentration of the one ormore components of the acid is from about 1 part per million to asolubility limit of the components in the mixture.
 4. The method ofclaim 1 wherein more than one carboxylic acid having an aqueous acidicdissociation constant of at least 1×10⁻⁶ is present in the mixture. 5.The method of claim 1 wherein the carboxylic acid is a monocarboxylicacid.
 6. The method of claim 1 wherein the carboxylic acid is adi-carboxylic acid.
 7. The method of claim 1 wherein the carboxylic acidcomprises at least three carboxylic acid groups.
 8. The method of claim1 wherein the carboxylic acid is trichloroacetic acid.
 9. The method ofclaim 1 wherein the carboxylic acid is maleic acid.
 10. The method ofclaim 1 wherein the carboxylic acid is citric acid.
 11. The method ofclaim 1 wherein the mixture is a solution, and wherein the organicsolvent consists of one or more members selected from the groupconsisting of alcohols, ketones, ethers and esters.
 12. The method ofclaim 1 wherein the mixture is a solution, and wherein the organicsolvent consists of an alcohol present in the solution to aconcentration of at least about 90%, by weight.
 13. The method of claim1 wherein the mixture is a solution, and wherein the organic solvent isisopropyl alcohol present in the solution to a concentration of at leastabout 90%, by weight.
 14. A method for reducing roughness induced on asilicon-dioxide-containing surface during removal ofsilicon-dioxide-containing debris with a cleaning solution, comprisingincorporation within the cleaning solution of one or more components ofa carboxylic acid having an aqueous acidic dissociation constant of atleast 1×10⁻⁶.
 15. The method of claim 14 wherein more than onecarboxylic acid having an aqueous acidic dissociation constant of atleast 1×10⁻⁶ is incorporated into the cleaning solution.
 16. The methodof claim 14 wherein the carboxylic acid is a monocarboxylic acid. 17.The method of claim 14 wherein the carboxylic acid is a di-carboxylicacid.
 18. The method of claim 14 wherein the carboxylic acid comprisesat least three carboxylic acid groups.
 19. A semiconductor processingmethod, comprising: providing a semiconductor substrate having an oxidesupported thereon; etching at least one opening which extends at leastpartially through the oxide, the etching leaving debris within theopening; and utilizing one or more components of a carboxylic acidhaving an aqueous acidic dissociation constant of at least 1×10⁻⁶ duringcleaning of at least some of the debris from within the opening.
 20. Themethod of claim 19 wherein the oxide consists of silicon dioxide ordoped silicon dioxide.
 21. The method of claim 19 wherein more than onecarboxylic acid having an aqueous acidic dissociation constant of atleast 1×10⁻⁶ is utilized during the cleaning.
 22. The method of claim 19wherein the carboxylic acid is present within a mixture during thecleaning; and wherein a total concentration of the one or morecomponents of the carboxylic acid within the mixture is from about 1part per million to a solubility limit of the components in the mixture.23. The method of claim 22 wherein the mixture includes at least oneorganic solvent selected from the group consisting of alcohols, ketones,ethers and esters.
 24. The method of claim 22 wherein the mixtureincludes an alkyl alcohol.
 25. The method of claim 24 wherein thealcohol is isopropyl alcohol.
 26. The method of claim 25 wherein themixture is a solution, and wherein the isopropyl alcohol is present inthe solution to a concentration of at least about 90%, by weight. 27.The method of claim 22 wherein the mixture is a solution comprising:isopropyl alcohol present to a concentration of at least about 90%, byweight; water; fluoride ions; and cations.
 28. The method of claim 27wherein the cations consist essentially of NH₄.
 29. A method of forminga capacitor construction; providing a semiconductor construction thatincludes a conductive node and an oxide over the node, the oxideconsisting essentially of silicon dioxide or doped silicon dioxide;etching an opening through the oxide to expose the conductive node, theetching leaving debris within the opening; utilizing one or morecomponents of a carboxylic acid having an aqueous acidic dissociationconstant of at least 1×10⁻⁶ during cleaning of at least some of thedebris from within the opening; after the cleaning, forming a firstcapacitor electrode within the opening; forming capacitor dielectricover the first capacitor electrode; and forming a second capacitorelectrode over the capacitor dielectric and capacitively coupled withthe first capacitor electrode.
 30. The method of claim 29 wherein morethan one carboxylic acid having an aqueous acidic dissociation constantof at least 1×10⁻⁶ is utilized during the cleaning.
 31. The method ofclaim 29 wherein the carboxylic acid is a monocarboxylic acid.
 32. Themethod of claim 29 wherein the carboxylic acid comprises at least twocarboxylic acid groups.
 33. The method of claim 29 wherein thecarboxylic acid is present within a mixture during the cleaning; andwherein a total concentration of the one or more components of thecarboxylic acid within the mixture is from about 1 part per million to asolubility limit of the components in the mixture.
 34. The method ofclaim 33 wherein the mixture is a solution comprising, in addition tothe components of the acid: an organic solvent consisting of one or moremembers selected from the group consisting of alcohols, ketones, ethersand esters; the organic solvent being present to a concentration of atleast about 90%, by weight; fluoride ions; and ammonium ions.